144 LECTURE IX. 



dioxide and water. It is well known that formic aldehyde 

 is a substance which readily undergoes polymerisation, so 

 that a carbohydrate might be easily derived from it thus 



6 CH 2 O = C 6 H 12 O 6 (grape-sugar) 

 and C 6 H 12 O 6 - H 2 O = C 6 H 10 O 5 (starch). 



Baeyer considers that the carbon dioxide is decomposed into carbon 

 monoxide and oxygen, and that the carbon monoxide combines with 

 hydrogen, derived from water, into formic aldehyde. 



rt, CO 2 =CO + O, 



b. CO + H 2 O = CH 2 O + O. 



Erlenmeyer, whilst accepting this view, considers, on chemical grounds, 

 that the process is effected somewhat differently ; that formic acid is first 

 produced together with hydrogen peroxide, 



and that then the formic acid and hydrogen peroxide are decomposed 

 formic aldehyde and water being formed and oxygen evolved, 



CH 2 O. 2 +H 2 O 2 = C 



It must be admitted that Just's observation that green plants cannot 

 assimilate carbon monoxide is unfavourable to this hypothesis, but it 

 must be borne in mind that the absorption of carbon monoxide from 

 without and the formation of it in the plant may involve very different 

 chemical conditions. 



Such a derivation of carbohydrate from formic aldehyde 

 is not entirely theoretical, for Butlerow has found that by the 

 action of alkalies upon a polymer of formic aldehyde, a sac- 

 charine substance (methylenitan) is produced : similarly from 

 trioxymethylene (C 3 H 6 O 3 ), Renard has obtained a syrupy 

 substance which has the formula C A H, Q O A , and which reduces 



6 12 6 



Fehling's solution. 



The facts do not, however, suffice to prove that the starch 

 formed in the chlorophyll-corpuscles under the influence of 

 light is actually derived from carbon dioxide and water. All 

 that has been proved is this, that a substance is formed which 

 has the ultimate chemical composition of a carbohydrate. 



In order to thoroughly understand the formation of 

 starch in chlorophyll-corpuscles, we must become acquainted 

 with the mode in which carbohydrate is formed elsewhere in 



